question about secondary class change

if i change my secondary class do i have to use skill points only to get all the skills for the new class?

I'm pretty sure you can go back and do quests to get most of the skills, but I'm sure that you have to buy some with points.

After you change you will have access to the profession's only quests - quests that can only be done by your new secondary. But since you can get skills from other quests as well you will have to buy some.
But since you should have a basic idea about which u skills you want to have it doesnt cost many skill points. I bought like 10 after i switched my secondary and already got these back from XP rewards